A load control method of a PLC analog output module includes a method of controlling a load by an analog current signal and a method of controlling a load by an analog voltage signal, and these methods respective have advantages and disadvantages as described below.
An analog current signal has strong resistance to noise and has the same current value at any position in a control loop that does not branch in the middle, and thus even a remote load can be accurately controlled. However, because it is a current control, its current consumption is large.
On the other hand, an analog voltage signal is vulnerable to noise and a voltage drop occurs due to resistance components of an electric cable and a terminal, and thus a remote load cannot be controlled accurately. However, because it is a voltage control, its current consumption is small.
In a PLC analog output module used in a PLC system where high reliability is required, occurrence of abnormalities such as disconnection of output wiring and short circuit of an output circuit needs to be detected. In this regard, in the PLC analog output module that uses the method of controlling a load by an analog voltage signal, there has been known a technique of detecting occurrence of abnormalities (see, for example, Patent Literature 1).